First Financial Investment Fund Annoying and irritating multiple phone calls regarding a "COMPLAINT from CITICORP." Atlanta, Tampa Georgia, Florida

I've been receiving MULTIPLE CALLS each week from "FIRST FINANCIAL INVESTMENT FUND" regarding a debt complaint from CITIBANK, regarding a Credit Card balance that was PAID IN FULL  ON 9/12/2014 to Account Discovery Systems LLC.
I have in my posession a letter from ADS, indicationg my BALANCE IS *ZERO* "RECEIPT OF FINAL PAYMENT FOR ACCOUNT SETTLED FOR LESS THAN THE FULL BALANCE."

I do NOT OWE CITIBANK ONE CENT -- BALANCE AGREED TO, AND PAID IN FULL -- yet FOUR YEARS LATER, THEY CALL ME ABOUT  A COMPLAINT ON THIS MATTER...MULTIPLE TIMES EACH WEEK.